I had the same happen to a pair of compact binoculars. It is the outer "soft" coating that has turned sticky (partially dissolved).....probably from heat. The only cure is to use a petroleum-based solvent (I used carb cleaner) and clean off all of the guck - that is, take off all of the coating. It will be a messy job - and take awhile to get it all off.
Once the coating has been removed, you'll have a serviceable unit, but it won't look very good. So, you could paint it, or something like that.